A car, usually an old American car (1930's-1970's) who seems determined to skin, slice, and slash the hands of every mechanic who touches it, regardless of their skill-level. Resistant to tools, penetrating oils, vice grips, and laws of physics. Any bolt that is in this car will STAY in this car, whether you want it there or not, and if you try to remove it, it WILL break off, and leave you requiring 15 stitches in the process.

Holy Hell.........that '49 Mercury just tore my whole hand open, and all I was trying to do was change her damn oil!! What a knucklebuster!!

One who likes to work on his own shit yo. One who likes to have split knuckles with blood and greese all over his/her hands. Like to say take a muffler off yo with a hammer and chisel and a cut off saw at 3:00 in the morning while the neighbors sleep. Knucklebusta yo

Like when your taking off a rusty U-clamp bolt from a muffler with a ratchet and you apply full force and the bolt snaps off forcing your hand full force into a jagged rusty piece of metal on the frame or some shit.

Usually pertaining to butch lesbians, a knucklebuster is someone who forcefully, and rapidly inserts their fingers (usually 2-3) into a woman's vagina, and in doing so they injure the joints of said fingers. Medically speaking, it's usually a small strain in a joint, not a knuckle, but the nomenclature holds steadfast.

A derogatory reference to a lesbian, or a girl who won't put out right away

The direct result of hardcore "fingerbanging"

Dude A: Did you hook up with that girl?
Bummed Dude: No, she was a goddamned knucklebuster